Process for preparing methylhydrazine



United States Patent 3,110,730 PROCESS FOR PREPARING METHYLI-IYDRAZINE Gabriel Gever, Scott St, flxford, N.Y., and John C. Howard, 13 Brown Ave, Norwich, N .Y. No Drawing. Filed June 13, 1960, Ser. No. 35,392 1 Claim. (Cl. 260 -533) This invention relates to a novel process for preparing methylhydrazine. More particularly, the present invention relates to a process for the preparation of methylhydrazine from 2-hydrazinoalcohols.

Methylhydrazine is useful as an intermediate in the preparation of pharmacologically active substances; e.g., S-nitrO-Z-furaldehyde 2-methyl semicarbazone; in the preparation of herbicides; and as a reducing agent.

We have made the surprising discovery that it is possible to prepare methylhydrazine very readily by the thermal decomposition of Z-hydrazino-alcohols. The pyrolysis proceeds straightforwardly in ordinarily available processing equipment. The starting materials are readily procurable at modest cost.

In accordance with our invention a Z-hydrazinoalcohol is placed in a suitable reaction vessel and heat supplied to cause decomposition. The desired end product of the decomposition, methylhydrazine, is collected by distillation. A schema representative of the course of our invention is as follows:

In the practice of our invention a Z-hydrazinoalcohol, for instance, Z-hydroxyethylhydrazine or Z-hydroxypropylhydrazine, is placed in a suitable reaction vessel which is adapted for distillation. Heat is supplied externally for about 1 to 6 hours. A temperature of from about ZOO-225 C. causes decomposition of the Z-hydrazinoalcohol. The liquid decomposition products are collected as the distillate. This distillate is further fractionated, preferably at reduced pressure, to obtain an azeotropic mixture of methylhydrazine and water which is dried with a suitable drying agent such as sodium hydroxide and further distilled at atmospheric pressure to obtain methylhydrazine.

In the practice of our invention we have found the addition of an inert high boiling diluent such as polyethylene glycol 400 to the reaction vessel containing the 2-hydrazinoalcohol prior to pyrolysis to be advantageous in mitigating too violent decomposition which sometimes occurs.

The method which we now prefer consists in placing 2- hydroxyethylhydrazine in a suitable reaction vessel, adding polyethylene glycol 400 as an inert heat absorbing medium and heating the vessel at a temperature of from 215220 C. for about one hour. The collected distillate containing methylhydrazine is distilled in vacuo and the fraction distilling at room temperature at 14 mm. of mercury pressure is collected. This fraction consisting essentially of water and methylhydrazine is redistilled at atmospheric pressure and the distillate therefrom is dried over sodium hydroxide while heating at a temperature of from 75-90" C. It is then fractionated through a suitable column,

such as a Vigreux, and the desired product, methylhydrazine, obtained.

3,1 10,730 Patented Nov. 12, I963 "ice In order that our invention may be readily available to and understood by those skilled in the art the following examples are illustrative:

EXAMPLE I Thermal Decomposition of 2-Hydroxyethylhydrazine In a 200 ml. flask set up for distillation and having a gas outlet tube connected to a trap containing dilute hydrochloric acid is placed 116 g. (1.53 moles) of Z-hydroxyethylhydrazine. The flask is heated in an oil bath to a temperature of 2l5220 C. for about one hour. A total of 75.5 g. of distillate is collected in this time.- This distillate is distilled in vacuo. A fraction (I) 39.2 g. distilling at room temperature at 14 mm. of mercury, and a smaller fraction (II), 2.3 g. having a boiling point of 50 C. at 3.0 mm. of mercury are obtained. Fraction I is redistilled at atmospheric pressure yielding 35.1 g. of a liquid having a boiling range of 81-104 C. and consisting essentially of methylhydrazine and its water azeotrope. This liquid is dried over sodium hydroxide at steam bath temperature and then distilled at atmospheric pressure through a Vigreux column giving 13.9 g. of methylhydrazine, boiling point 8687 C.

EXAMPLE II Thermal Decomposition of 2-Hydroxypropylhydrazine In a 500 ml. fiask equipped with a stirrer, thermometer, a gas outlet tube leading to an acid trap and a variable take-off assembly is placed 301 g. (3.34 moles) of 2-hydroxypropylhydrazine. The flask is heated to 210 C. with a mantle. After 5 /2 hours 187 g. of distillate having a boiling range of 125-145 C. are collected. During the distillation a reflux rate of 3:1 is used. The bulk of the distillate, 164 g, is distilled through a Vigreux column. The distillate having a boiling range of 95108 and amounting to 112 g. is dried over sodium hydroxide at room temperature for eight hours. The organic layer is decanted and further dried over sodium hydroxide at refrigerator temperature for 12 hours. The organic layer is filtered through glass wool and then distilled through a Vigreux column. Two fractions are obtained: I having a boiling point of -86 C. and amounting to 9.5 g. is methylhydrazine; and II having a boiling range of 929 7 C. and amounting to 31 g. which is a methylhydrazine derivative readily converted to methylhydrazine by treatment with dilute acid.

What is claimed is:

A process for preparing methylhydrazine by thermal decomposition of a Z-hydrazinoalcohol selected from the group consisting of 2-hydroxyethylhydrazine and 2-hydroxypropylhydrazine, which comprises subjecting said hydrazinoalcohol to exothermic thermal decomposition at a temperature of from about 200 to 225 C., collecting the liquid distillate and recovering methylhydrazine therefrom by redistillation.

References Cited in the file of this patent Gabriel: Ber., Vol.47, pp. 302833 (1914), C.A. 9321. 

